1. Field of the Invention
The present invention relates to a refractory system for use in reactors for producing carbon black.
2. Description of the Prior Art
It is known to produce carbon black in commercial quantities by cracking a hydrocarbon feedstock material, such as natural gas (containing a mixture of one or more of methane, ethane, propane and butane gases), refinery bottoms, etc. to obtain carbon black and hydrogen gas. When methane is employed, the reaction may be represented by the equation: EQU CH.sub.4 .fwdarw.C+2H.sub.2 +(trace quantities of aromatic compounds, illuminant gases and uncracked methane)
Known commercial processes for cracking methane to form carbon black, commonly referred to as `thermal black`, comprise the steps of heating a checkerwork of refractory bricks in a reactor to a temperature of about 2700.degree. F. and then passing the feedstock methane through the checkerwork in an essentially oxygen free environment. During the reaction, the methane is cracked into a mixture of thermal black, hydrogen gas and trace amounts of undesired byproducts. To drive the endothermic cracking process, energy (heat) is removed from the refractory bricks during the cracking operation, thereby reducing the temperature of the bricks. When the temperature of the refractory bricks is lowered to about 1200.degree. F., the reaction must be terminated to allow the refractory bricks to be reheated to the desired temperature.
Problems exist with the known processes in that some thermal black accumulates on the refractory brick and degrades the thermal transfer process, both during the heating of the bricks and during the cracking of the methane. It has been determined that this degradation reduces the efficiency of the thermal black production process, reducing the yield and increasing the cost of the final product. A further problem exists with known processes in that, at the operating temperatures within the thermal black reactor, the accumulated thermal black eventually reacts with the generally silica-based material of the refractory bricks causing erosion and/or breakdown of the bricks. This breakdown necessitates that the reactors be `re-bricked` sooner, and thus more often, than would otherwise be the case. Moreover, rebricking requires the reactor to be shut down for relatively long periods of time and incurring a significant cost for the labour and materials to effect the re-bricking. Further, as the refractory bricks erode and breakdown, the eroded refractory material tends to contaminate, and thus lower the quality of, the thermal black final product.